Composition of cellulose and an alkali biuret metal complex



United States PatentO COMPOSITION OF CELLULOSE AND AN ALKALI BIURET METAL COMPLEX Leslie L. Balassa, Madison, NJ.

No Drawing. Application September 8, 1953 Serial No. 379,093

7 Claims. (Cl. 106-203) This invention relates to the composition of cellulose solutions with compositions of the alkali-biuret-copper type and related compositions.

Cellulose solutions made principally by the viscose process or by the cuprammonium process, have been employed for many years in the manufacture of regenerated cellulose articles such as rayon fibers, films of the cellophane type, cellulose sponges, and many other objects. The shortcomings especially of the fibers obtained by the viscose process have been extensively investigated throughout the past half century. The cuprammonium process produced fibers which were superior in some respects to those obtained by the viscose process but the former process is more expensive and requires extensive installation of equipment for the recovery of the expensive and often scarce copper and of the volatile and toxic ammonia. It has been found very diflicultin the case of the cuprammonium process to completely eliminate the health hazards connected with the use of large quantities of ammonia; and in the case of the viscose process, the handling of large amounts of carbon bisulfide poses in addition to the health hazard, (also fire and explosion hazards. Furthermore, the regenerated cellulose articles, especially the fibers and :films obtained by either of the above processes, lose :strength to an excessive degree when immersed in water.

The present invention completely eliminates many of the shortcomings of the viscose and cuprammonium processes and reduces markedly a number of other objec- 'tionable features inherent in these processes, as will be described below.

This invention relates to the composition of cellulose solutions prepared by the use of alkali-biuret-copper complexes. The cellulose fibers and filmsprepared in accordance with this invention possess higher wet strength than has been possible to obtain with the conventional viscose and cuprammonium processes. Regenerated cellulose articles so produced have greater chemical resistance than was possible to obtain by the use of the cuprammonium or the viscose processes.

A further advantage afiorded by this invention is the production of a cellulose product, such as a cellulose fihn, filament, or fibre, in which there is intimately bound or entrained within the finished cellulose structure itself a copper or a nickel compound. While the precise chemical or physical relationship between the copper or nickel atoms and the cellulose molecule is not entirely understood at the present time, it is possible by this invention to produce a cellulose strand or fibre in which extremely finely divided, perhaps down to a molecular order, cop per or nickel compounds are intimately and firmly bound to the cellulose within the cellulose structure. This product in and by itself, presumably due to the presence of copper or nickel ions, has advantageous properties of resistance to molds or mildew or other microbiological growths, including those of parasitic nature. The presence of nickel or copper in the cellulose also permits inti 2 mate bonding of addition compounds with the cellulose. For example certain acids and other compounds which react with copper or nickel to form insoluble compounds may become bound to the cellulose fibers. Other compounds Which may thus be intimately bound to the cellulose fiber are dyestuffs which are capable of forming lakes with copper or nickel.

In accordance with this invention, a suitable grade of cellulose such as purified Wood pulp, cotton, etc. is dissolved or dispersed in an alkali-biuret-copper solution; it is then preferably aged, filtered and deaerated, then it may be shaped by spinning it through suitable spinnerets, or by extruding it through slots, jets or other devices into a setting bath which may or may not contain a cellulose across linking agent, the filament or film being preferably subjected to considerable tension to impart a certain degree of stretch as it passes through the setting bath or shortly thereafter. The cellulose is then regenerated and the chemicals are removed by washing, preferably with Water and dilute acids, until substantially all the copper is removed. The final drying and treating of the filaments and films may be accomplished in a manner customary to the art. While I have described the cellulose as being dissolved or dispersed in said solution, I desire it to be understood that I use the term solution herein to include either a state of colloidal dispersion or solution and I do not Wish to be bound by any theoretical considerations as to the precise nature of the preparation.

According to this invention, it has been found that satisfactory cellulose solutions for the purposes indicated can be obtained from cellulose or preferably alkali cellulose by the use of biuret, a copper compound, and an alkali metal hydroxide. When a solution of biuret mixed with a copper compound is treated with an alkali metal hydroxide, they form a complex which has a strong solvent or dispersing action on cellulose fibers. l have found that nickel compounds may be employed in place of copper but with less efiectiveness than the copper compounds. In the practice of this invention most water soluble salts and some water insoluble compounds of copper or nickel may be employed such as the chlorides, sulfates, nitrates, acetates, etc. It is the metal ion of the group consisting of copper or nickel which is important for the purpose of this invention rather than the particular anion with which it is associated. It is the combination of the biuret with the copper or nickel in the alkaline aqueous medium that forms the combination which is the effective cellulose solvent. This combination is a soluble complex formed in the alkaline aqueous medium between the metal and the biuret. Accordingly, for the purpose of this invention, any copper or nickel compound may be employed that forms with biuret in the presence of an alkali metal hydroxide in an aqueous medium, a metal biuret complex.

By Way of further example, freshly precipitated copper hydroxide or nickel hydroxide, each of which is substantially water insoluble, is capablein the presence of alkali metal hydroxide in an aqueous medium of forming an alkali soluble complex with the biuret and therefore may be employed. Moreover, essentially water insoluble salts of copper and nickel such as cupric phosphate or basic copper sulfate are reactive withbiuret in an aqueous medium in the presence of an alkali metal hydroxide and may be employed. However, in practical application, it is preferable to employ a water soluble salt of copper or nickel. More generally, the metal biuret complex dissolved in the alkali metal hydroxide solution is referred to herein for the sake of brevity as A-B-C for the alkali biuret copper or A-B-N for the alkali-biuret-nickel complex solution as the case may be.

The reagent concentrations used in this invention may be relatively low, apparently because of the relative solubilities of the chemicals useful in forming the effective cellulose dispersing complex. Thus in order to produce a solution of the biuret at the temperatures employed in the process, suflicient alkali metal hydroxide must be present to provide at least about 1 molar concentration, i.e., at least about 1 mol of the alkali metal hydroxide per liter. On the other hand, when the molar concentration of the alkali metal hydroxide approaches about 6 mols per liter, the solubility of the biuret complex with either copper or nickel becomes reduced. Accordingly,

the solution concentrations of the alkali metal hydroxide ranges from about 1 to 6 mols per liter. Such concentrations of alkali metal hydroxide may be composed of one or more metal hydroxides. The preferred alkali metal hydroxides are sodium hydroxide and potassium hydroxide. Generally, in the preferred practice of this invention the concentration of the alkali metal hydroxide is of the order of l to 4 mols per liter.

The solution concentration of the biuret may vary from about 0.5 to about 100 grams/liter although it is preferable in the practice of this invention that the solution concentration of the biuret be of the order of 20 to 50 grams/liter. It should be noted in this connection that the molecular weight of biuret is 103: hence A of the value of biuret concentration in terms of grams per liter indicates the approximate molar concentration. The preferred molar concentration of biuret is about 0.2 to 0.5 mol per liter.

As regards the metal, i.e. copper or nickel, which is used may be from about .6025 to 0.25 mol per liter; the preferred concentration being of the order of 0.1 to 0.2 mol per liter. While ordinarily only a single metal compound is used in carrying out this invention, two or more may be employed for it is important only to have the required amount of metal available from any one or more compounds of copper or nickel. The metal compound that is preferably employed is copper sulfate.

The purified cellulose fibers or pulp may be subjected to the solvent action of the alkali biuret copper solution for periods ranging from ten minutes to several hours and at temperatures ranging from the freezing point of the solution up to about 25 C. The solvent action of the A-B-C solution is influenced both by temperature and by the concentration of the ingredients in the solvent mixture. The solvent action of the A-B-C solution towards cellulose is greater at lower temperatures than at higher temperatures with the solvent action being substantially completely lost when the temperature of the A-B-C solution reaches about 50 C. or higher. When the concentration of the metal and biuret drops below the minimum mentioned above, the solvent capacity of the A-B-C solution towards cellulose is greatly reduced. The alkali,

metal and biuret concentrations as well as the temperatures employed in the process may be governed by considerations of economy, by the type of cellulose used, by the concentrations of final cellulose solutions, and by the requirement of suitable strength characteristics in the finished product, as may be desired or required.

The cellulose solutions are conveniently. prepared in shredders or mixing tanks equipped with a heavy duty scroll mixers inside. The tanks are equipped with jackets or coils to provide suliicient cooling surface for maintaining the desired temperature. The cellulose solution is conveniently prepared by introducing the cellulose first into the mixing tank, then adding sufficient alkali to moisten the cellulose and finally introducing the premixed biuret copper slurry. The remainder of the required alkali and water is then introduced while the mixing is continued until the desired chemical concentration is obtained. The temperature of the mix, which normally rises during the preparation of the mix, is then brought down to the desired degree, and the mixing continued until a homogeneous solution is obtained. The cellulose solutions thus obtained may range in cellulose content up to 8%. However, higher cellulose concentrations may also be obtained by careful control of the composition of the mix, the chemical concentrations and temperatures.

Cellulose solutions of practical concentrations obtained in the above manner are generally too high in viscosity for use in fiber spinning or in film spreading or extrusion processes. The viscosity of these solutions may be brought down to a convenient point, e.g. 1500 ops, by oxidation with air, or with peroxides or similar oxidizing agents. After the desired viscosity is obtained, the cellulose solutions are deaerated, filtered, and then spun through suitable spinnerets or cast or extruded through suitable nozzles.

In controlling the viscosity of the cellulose solutions via oxidation, the effect of the peroxides or other oxidizing agents may be stopped by the use of reducing agents such as bisulfites, hydrosulfites, etc. such as sodium bisulfite or sodium hydrosulfite, or such as hydroxylamine. If necessary, the cellulose solutions may be st-abilized by the incorporation of a small percentage of glucose or tartrates e.g. tartaric acid which forms sodium tartrate, or similar polyhydroxy compounds.

Upon spinning or extruding the cellulose solutions, the resulting fibers or films are passed through a setting bath which may contain a low percentage of an alkali or it may be a strong or a mild solution of an acid. If the setting bath is an alkali, it may, optionally, contain a material which is capable of cross-linking the cellulose molecule. Suitable cross linking agents are organic halogen compounds containing at least two reactive halogens, one on each of two carbon atoms, compounds containing both halogen and epoxy groups such as epichlorohydrin, diisocyanates, dichlorohydrin, dichlorodiethyl ether, hexamethylene diisocyanate, or the like. The cross linking agents if they are alkali stable may be employed in the same bath together with the alkali. If they cannot be dispersed in the alkali or if they are hydrolyzed by the alkali, they may be employed either in a neutral aqueous solution or dispersion or in an organic solvent, or even in a vapor phase applied to the cellulose filament or film before it reaches a subsequent bath.

The cellulose filaments or films may be stretched either before or during or even shortly after leaving the setting baths. Mechanical stretching devices are available and well known in this art.

The cellulose articles emerging from the setting bath are washed with water, then with acid, to remove substantially all the copper, and finally with water until substantially all the acid is removed. The cellulose articles are then dried and treated in a manner customary to the art.

The chemicals used may be recovered by suitable means which will be the subject of future patent applications.

The acids suitable for removing the copper or nickel from the cellulose articles leaving the setting bath are those which form water soluble salts with copper or nickel: thus any suitable acid may be employed; either mineral or organic, such as sulfuric, hydrochloric, nitric, acetic, formic or oxalic. Ordinarily in practicing this invention a 4% to 10% solution of sulfuric acid is used for the purpose and then the fibers or other cellulose articles are washed so as to remove any unreacted acid as well as other soluble substances.

While the cellulose fibers or pulp may be dissolved in the A-BC reagent by dissolving the essential ingredients thereof in a common solution with which the cellulose is contacted, the cellulose will be dissolved whenever and however the essential ingredients are caused to occur in contact with it in an aqueous medium. Thus the cellulose may first be treated with a slurry containing biuret and a copper salt and thereafter treated with a solution of an alkali metal hydroxide which reacts with the biuret and the copper salt to produce alkaline biuret copper for effectively dissolving the cellulose.

It is unnecessary to employ pure biuret in the practice of this invention. For example, the products of pyrolysis of urea, especially when this pyrolysis is done under conditions such that the yield of biuret is high while that of unreacted urea and that of by-products of pyrolysis is relatively low, may be used without further purification. In any case, it is the biuret which is essential, for without biuret there is no noticeable solvation of the cellulose. Moreover, in the absence of suitable copper ornickel compounds, the biuret dissolved in the alkali metal hydroxide is without eifect on cellulose.

A convenient and economical source of biuret for use in the process of this invention is the product of reaction obtained by heating urea to about 160 C. for 1 to 1% hours under reduced pressure corresponding to 20 to 25 inches of vacuum, the entire product of reaction being used without attempting to separate the biuret from unreacted urea or other reaction by-products such as cyanuric acid and ammelide. The content of biuret contained in the reaction product is determinable by analysis, and sufiicient of the reaction product is employed so that the biuret content thereof will provide the desired amount of biuret in the solution to be used for cellulose solvation. Biuret, in relatively pure form, or in admixture with varying amounts of unreacted urea and any of the by-products of urea pyrolysis, is defined herein as technical biuret obtained by urea pyrolysis. Such technical biuret preferably contains at least about 50% of biuret and is employed in the preferred practice of this invention. The technical biuret can be produced for use according to this invention at materially lower cost as compared with pure biuret and while it contains a substantial amount of unreacted urea, which is entirely without effect in the absence of the biuret, likewise has been found to have no detrimental efiect when it is present in addition to the biuret during the solvation of the cellulose.

In preparing a solution containing biuret, metal compound, and alkali metal hydroxide, it is preferable to first mix the biuret, whether pure or not, with the metal compound in an aqueous medium, and thereafter add the alkali metal hydroxide with stirring, as, for example, by adding a 50% aqueous solution of alkali metal hydroxide and finally bringing the solution to the desired concentration by dilution with water. While the constituents may be combined by dissolving the biuret in alkali metal hydroxide solution and then adding the metal compounds, that method involves the danger of converting the metal to an insoluble oxide. The metal compound in any case should not be added directly to the alkali metal hydroxide due to a tendency in such case to form insoluble metal oxide.

The nature of the process of this invention and its objectives and advantages will be more thoroughly understood upon consideration of the examples below set forth. It is to be understood that the following examples are illustrative and explanatory only, and are not to be construed as limiting the scope of this invention or of the appended claims.

PREPARATION CELLULOSE SOLUTIONS Example 1.-5% cellulose solution.

A-B-C solution: NaOH, 1.5 mole-biuret, 0.3 mol-- copper, 0.15 mol. Parts by weight Preparation-The basic copper sulfate and the biuret were slurried in the water and then the sodium hydroxide was added while mixing. The mixing was continued until a complete solution of the copper sulfate and the biuret 6 was obtained. The solution was allowed to stand over night and then the precipitated iron hydroxide formed from the iron impurities present was removed by centrifuging. The bleached cotton linters were added gradually under constant mixing. The mixture was then cooled to 5 C. and the mixing continued for about 20 minutes when a viscous solution of the cellulose was obtained essentially free from undissolved fibers.

Example 2.5% cellulose solution. A-B-C solution. NaOH, 2 mols-biuret, 0.3 molcopper, 0.15 mol.

Parts by weight Water 300 Basic copper sulfate (40% Cu) 24 Biuret 31 Sodium hydroxide (50% NaOH) solution 160 Bleached cotton linters 55 Ice 500 Total 1070 Preparation-The basic copper sulfate and the biuret were slurried in the water and then the sodium hydroxide was added and mixed until the copper compound and the biuret were dissolved. The bleached cotton linters were then introduced into the solution and thoroughly wetted out and mixed. The cracked ice was then added and mixed until it melted in the mixture. The temperature of the mixture was brought down to somewhat below 0. C. An essentially complete solution of the cotton linters was obtained within a few minutes of reaching 0 C.

Preparati0n.--The basic copper sulfate and the pyrolyzed urea were slurried in the water, then the bleached cotton linters were introduced, thoroughly mixed, and then the sodium hydroxide was added under constant mixing. The mixture was then cooled to below 0 C. i.e. approximately to -5 C., and mixed for about 20 minutes when a homogeneous solution was obtained.

Example 4.5% cellulose solution.

A-B-C solution. Same as Example 1.

Parts by weight Water 804.2 Cuprous chloride (50% Cu) 19.2 Pyrolyzed urea (50% biuret) 62 Bleached cotton linters 55 Sodium hydroxide (50% NaOH) solution Total 1060.4

Preparati0n.-The cuprous chloride and the pyrolyzed urea were slurried in water, then the bleached cotton linters were introduced, thoroughly mixed, and then the sodium hydroxide added under constant mixing. The mixture was then cooled to -3 C. and mixed for a further 20 minutes when a homogeneous solution was obtained.

Example 5 .-5% cellulose solution. A-BC solution. Same as Example 1.

Parts by weight Preparatin.--The cellulose pulp was broken up into small pieces and then slurried in the water. Then the sodium hydroxide was added, mixed, and the mixture cooled to about C.

The biuret and the basic copper carbonate were slurried separately in the water, and then added to the cooled alkaline cellulose slurry. The mixture was then cooled further to below 0 C. while the mixing continued. The cellulose pulp went very rapidly into solution as the temperature dropped below 0 C.

Example 6.-5% cellulose solution.

AB-C solution. NaOH, 2 mols-biuret, .25 molcopper, .10 mol.

Parts by weight Water 300 Basic copper sulfate (40% Cu) 15.8 Biuret 26 Sodium hydroxide (50% NaOI-I) solution 160 Bleached cotton linters 55 Ice 500 Total 1056.8

Preparati0n.It was handled in the same manner as Example 2. The cotton linters went into solution somewhat slowly, but after somewhat more prolonged mixing (approximately for an hour), a satisfactory solution was obtained.

Example 7 .7% cellulose solution.

AB-C solution. Same as Example 2.

Parts by weight Cellulose pulp (30% dry cellulose) 233 Water 100 Sodium hydroxide (50% NaOH) solution 160 Ice 250 Biuret 31 Basic copper sulfate (40% Cu) 24 Water 200 Total 998 Parts by Weight Water 300 Basic copper sulfate (40% Cu) 24 Biuret 31 Potassium hydroxide (50% KOH) solution 224 Bleached cotton linters 55 Ice 436 Total 1070 Preparation.The cellulose solution was prepared in the same manner as described in Example 2. In this case, however, the cotton linters dissolved at a considerably slower rate than was the case in Example 2. It appeared to require somewhat prolonged, up to about 2 hours, mixing before a satisfactory solution was obtained.

Example 9.-3% cellulose solution.

A-B-N solution. NaOl-I, 2 mols-biuret, 0.3 molnickel (Ni), 0.15 mol.

Parts by weight Water 770 Nickel acetate (32% Ni) 27.5 Pyrolyzed urea (50% biuret) 62 Sodium hydroxide (50% NaOH) solution Bleached cotton linters 33 Total 1052.5

Preparation-The nickel acetate and the pyrolyzed urea were mixed with the water and then the sodium hydroxide was added while mixing. The mixing was continued until a solution of the nickel acetate and biuret was obtained. The bleached cotton linters were then added gradually under constant mixing, and then the mixture was cooled to 10 C. The mixing was continued for about an hour when a viscous solution of the cellulose was obtained, essentially free from undissolved fibers.

PREPARATION OF CELLULOSE FILA- MENTS AND FILMS Any of the cellulose solutions described in Examples 1 to 9 and others prepared in accordance with the teachings continued in this application may be used in the preparation of cellulose filaments and films. Since the viscosity of the solutions as prepared is too high for most spinning processes, I prefer to adjust the viscosity by oxidation, for example, by aeration, or preferably by the use of a solution of certain oxidizing agents such as ammonium persulfate, urea peroxide, hydrogen peroxide, or sodium hypochlorite. When using these agents I prefer to employ them in the form of solutions of low concentrations containing about 5% of the active agent. I add then about 1 to 2% of the 5% solution to the cellulose solution which in a short time reduces the viscosity of the cellulose solution. The amount of the above oxidizing agents when used as viscosity adjusters to control the viscosity may be varied as required to give the desired viscosity to the cellulose solution for extrusion or spinning. These oxidizing agents when used in form of dilute solutions apparently do not degrade the cellulose solutions to any appreciable extent.

After the cellulose solutions have been adjusted to the proper viscosity, they are filtered and extruded through suitable spinnerets when filaments are to be obtained or through nozzles or slots if films are desired. Examples 10 through 14 are illustrative of setting the extruded or cast films, threads, sheets or articles.

Setting baths Example 10.The setting or coagulation or precipitation of the films and filaments may be conveniently effected by spinning them or extruding them directly into a 4 to 5% sulfuric acid solution which simultaneously neutralizes the sodium hydroxide present and removes the biuret and the copper from the cellulose articles.

Example 11.A more economical setting bath is an inert atmosphere or bath water when employed at temperatures of over 50 C. preferably in the neighborhood of 70 C. Since the cellulose is insoluble in the A-B-C solution at temperatures over 50 C., the hot water will simultaneously insolubilize the cellulose gel by elevating its temperature and by diluting the AB-C solution in a very short time to a concentration below that where it is a solvent for cellulose. The hot water removes a substantial part of the sodium hydroxide, the biuret and partnofgthe copper which then may be conveniently recovered. The cellulose" articles containing still a substantial part of the copper have to be further treated with an acid bath to effectively remove substantially all the copper.

Example 12.-I have found that another satisfactory way to set the extruded cellulose solutions is to use a setting bath containing between 3% and of NaOH and having a temperature preferably not less than 50 C. This hath will set the cellulose in the same manner as the hot water bath but will dissolve a somewhat higher percentage of the biuret and copper contained in the cellulose and thereby make possible a more economical recovery of these valuable chemicals. Similar to the hot water treatment, this setting bath will not remove all the copper from the cellulose and therefore the final removal of the copper will have to'be accomplished by an acid wash. v

Example Ii-Setting by simultaneous cross-linking. I have been able to set effectively the extrudedcellulose filaments and films and at the same time cross-link some of the surface molecules of the cellulose and thereby create a tougher skin for the cellulose article by using as a setting bath, a 2% solution of borax which is considered to act as a temporary cross-linking agent.

Other setting baths of this nature containing permanent cross-linking agents such as epichlorohydrin, dichlorohydrin, dichlorodiethyl ether and hexamethylene diisocyanate were prepared by dissolving these reagents in a suitable solvent such as acetone or methyl-ethyl ketone or the like in which these agents are soluble and which themselves are partially soluble in water but will not react with the cross-linking agents. Suitable cross-linking setting baths may be obtained by preparing solutions of between 0.1% and 25% of the cross-linking agent in the solvent. A typical solution is 2% by weight of epichlorohydrin in acetone. The cellulose articles emerging from the cross-linking setting bath are first dried either in warm air or on a drum, then treated with hot water, and finally with acid to obtain essentially copperfree products.

Example 14.Setting and cross-linking in a fog chamber. The setting and cross-linking may be conveniently and most economically accomplished by extruding the cellulose into a chamber into which simultaneously metered quantities of a cross-linking agent is being introduced by atomizing it through suitable nozzles. In this manner fog chambers have been prepared containing 0.1% up to 25% of cross-linking agent in suspension and under vigorous agitation with air. The cellulose articles passing through these chambers pick up quantities of the cross-linking agent corresponding to the concentration of the cross-linking agent present and the time of their exposure to the cross-linking agent. The cellulose articles emerging from the fog chamber are preferably treated first with a warm 3 to 5% sodium hydroxide solution and finally the copper is extracted in a sulfuric acid bath.

Stretch spinning-It is evident to those acquainted with the art that most of the above setting processes can be readily combined with the stretch-spinning steps used in some cuprammonium and viscose rayon spinning processes. In this manner films and filaments may be oh tained with a well oriented molecular structure and showing the increase toughness and tensile strength characteristic of the stretch spun articles.

As stated above, this invention also contemplates the production of shaped cellulose articles in which one or more copper or nickel compound are permitted or caused to remain in the finished product after the biuret and alkali have been removed. The residual copper or nickel is contained Within the cellulose structure and may be present, in controlled amounts, in elfective quantity. It may be seen that amounts of copper or nickel, in compound form calculated on the basis of metal content are present in the foregoing examples up to approximately 10%, 12%, 14%, 25% by weight based on the cellulose. Of course these amounts may be increased by increasing the amount of copper or nickel salt in the initial solution and the residual amount of copper or nickel (calculated on the basis of weight of the metal) may run all the way from the order of traces up to 50% by weight, based upon the cellulose. Obviously, the initial amounts present may be reduced in controlled fashion by selective treatment with acid or other compounds which will combine with the copper or nickel to solubilize the copper or nickel, examples of such other compound being sodium thiosulphate, and complexing agents such as diethylaminotetraacetic acid. This selective retention of the copper or nickel may be effected by simply omitting the acid bath steps referred to in Examples 11 and 12 above. The regenerated cellulose material thus obtained, containing the copper or the nickel, exhibits desirable fungus-proofing or antimycotic characteristics. These desirable properties or characteristics may be further enhanced by reaction of the copper in the cellulose with other compounds such as 8-hydroxyquinoline or napthenic acid or certain long-chain fatty acids as, for example, undecylenic acid, thereby producing such materials as copper-S-hydroxyquinolinolate or copper-naphthenate, or copper-undecylenate, all of which exhibit mildew-resistant properties. Similarly, the cellulose made by the process of this invention and containing residually bound nickel may be treated with such or similar materials to form corresponding compounds having desirable protective properties against microbiological attack.

Other desirable advantages may be obtained by the process described above in which the copper or nickel which is intimately bound with the cellulose is treated or reacted with other types of compounds, for example, materials which combine with copper or nickel to form color lakes may be used for the production of desired or controlled color effects.

It is to be understood that the formation of such copper or nickel compounds need not be confined in point of time to the fabrication of the fibers themselves, but that the present invention permits the production of a finished fabric or film, woven or otherwise constructed from the material just described, which fabric or film may be treated with such desired compound at a later stage.

What is claimed is:

1. A coagulable cellulose solution comprising in said solution an alkali'biuret-metal complex in which the alkali is an alkali metal hydroxide and the metal is selected from the group consisting of copper and nickel.

2. A coagulable cellulose solution comprising water, cellulose and an alkali biuret metal complex, in which the alkali is present in a quantity from about 1 to about 6 mols of an alkali metal hydroxide per liter of said solution and the biuret is present in quantity of about 0.5 to about grams per liter of said solution and the metal is selected from the group consisting of copper and nickel and is present in quantity of about .0025 to about 0.25 mol per liter of said solution.

3. A coagulable cellulose solution comprising water, cellulose and an alkali biuret metal complex, in which the alkali is present in a quantity from about 1 to about 6 mols of an alkali metal hydroxide per liter of said solution' and the biuret is present in quantity of about 0.5 to about 100 grams per liter of said solution and the metal is copper and is present in quantity of about .0025 to about 0.25 mol per liter of said solution.

4. A coagulable cellulose solution comprising water, cellulose and an alkali biuret metal complex, in which the alkali is present in a quantity from about 1 to about 6 mols of an alkali metal hydroxide per liter of said solution and the biuret is present in quantity of about 0.5 to about 100 grams per liter of said solution and the metal is nickel and is present in quantity of about .0025 to about 0.25 mol per liter of said solution.

5. A coagulable cellulose solution comprising water, cellulose and an alkali biuret metal complex, in which the alkali is present in a quantity from about 1 to about 6 mols of an alkali metal hydroxide per liter of said solution and the biuret is present in quantity of about 0.5 to about 100 grams per liter of said solution and the metal is selected from the group consisting of copper and nickel and is present in quantity of about .0025 to about 0.25 mol per liter of said solution, said cellulose being present in quantity between about 3% to about 8% by weight based upon said solution.

6. A coagulable cellulose solution comprising water, cellulose and an alkali biuret metal complex, in which the alkali is present in a quantity from about 1 to about 4 mols of an alkali metal hydroxide per liter of said solution and the biuret is present in quantity of about 20 to about 50 grams per liter of said solution and the metal is selected from the group consisting of copper and nickel and is present in quantity of about .1 to about .2 mol per liter of said solution.

12 7. The composition of claim 2 in which urea is present in an amount up to the weight of the biuret present.

References Cited in the file of this patent FOREIGN PATENTS Great Britain of 1906 OTHER REFERENCES Rising et a1.: J. Biol. Chem. 89, l-8, 17 and 18 (1930). Copy in Sci. Lib.

Heuser: Cellulose Chemistry (1944), p. 148. Copy 20 in Div. 63. 

2. A COAGULABLE CELLULOSE SOLUTION COMPRISING WATER, CELLULOSE AND AN ALKALI BIURET METAL COMPLEX, IN WHICH THE ALKALI IS PRESENT IN A QUANTITY FROM ABOUT 1 TO ABOUT 6 MOLS OF AN ALKALI METAL HYDROXIDE PER LITER OF SAID SOLUTION AND THE BIURET IS PRESENT IN QUANTITY OF ABOUT 0.5 TO ABOUT 100 GRAMS PER LITER OF SAID SOLUTION AND THE METAL IS SELECTED FROM THE GROUP CONSISTING OF COPPER AND NICKEL AND IS PRESENT IN QUANTITY OF ABOUT .0025 TO ABOUT 0.25 MOL PER LITER OF SAID SOLUTION. 